1. Field
The present invention relates to a communication apparatus that communicates using a frame of multiple blocks and an allocation determining method in the communication apparatus. The present invention also relates to a communication apparatus and an allocation determining method for improving the transmission efficiency.
2. Description of the Related Art
Currently, the 3GPP (The Third Generation Partnership Project), a mobile communication standards body, is developing the LTE (Long Term Evolution) specifications for next-generation mobile communications. In the development of the LTE specifications, an example format, as illustrated in FIG. 8, is defined as a frame format for uplink communications.
As illustrated in FIG. 8, the frame format for uplink communications contains a plurality of blocks, in which data, control information or an RS (Reference Signal) is inserted into each block. An RS is pilot information that is used for estimating a channel. An RS includes a Sounding RS for measurement and a Dem RS for demodulation.
An RS is used to obtain a channel estimate value necessary to demodulate data or control information in a frame. The frame format in FIG. 8 shows that an RS is inserted into an SB (Short Block), and that the data or control information is inserted into an LB (Long Block). A communication apparatus performs processing, such as complementation or averaging, to determine a channel estimate value of an LB that is not adjacent to any SB.
However, even the complementation or the like cannot avoid variations in accuracy of channel estimation due to the LB position. That is, the channel estimation accuracy of LBs that are adjacent to an SB is the highest, and the channel estimation accuracy of the LB that is farther away from the SB is lower. For an LB with lower channel estimation accuracy, a transmission error is more likely to occur.
Japanese Laid-Open Patent Publication No. 2007-116427 proposes a technique to improve the transmission efficiency in communications via such a frame format. According to the technique, based on an assumption that an LB being nearer to pilot information has higher channel estimation accuracy, data of a user with higher propagation path property fluctuation velocity is allocated in an LB being near to pilot information, preventing degradation in receiving performance of the fast-moving user.
However, even the adjustment of an insertion position of data for each user, as disclosed in the related art above, cannot sufficiently improve the transmission efficiency. For example, if the control information for demodulation/decoding has not been normally transmitted and even if the data has been normally transmitted, it is still unavoidable that the data will be discarded because the demodulation/decoding of the data cannot be performed, resulting in a decrease in transmission efficiency.
Another example is that when much data needs to be retransmitted for some reason, if new data is normally transmitted but data to be retransmitted is not normally transmitted, many LBs will be used to retransmit the data. Because of this, fewer LBs can be used to transmit the new data, resulting in a decrease in transmission efficiency. The transmission efficiency decreases in both cases that much data needs to be retransmitted and that the retransmission related control information is not normally transmitted.